Faster Detailed Hydrocarbon Analysis (DHA) Using Hydrogen

Significance of the Topic

Accurate quantification of hydrocarbon and oxygenate components in gasoline is essential for optimizing refinery operations, ensuring regulatory compliance, and maintaining fuel quality. Detailed hydrocarbon analysis (DHA) provides the high resolution and reproducibility required for monitoring raw material compositions, controlling blending processes, and assessing additive levels. Improvements in column inertness, selectivity, and carrier gas efficiency directly translate into faster throughput and more reliable data for industrial and research laboratories.

Objectives and Study Overview

This study evaluates the performance of Restek’s Rtx-DHA-100 column under both helium and hydrogen carrier gases, comparing it to a competitor column. Key goals include:

• Verifying compliance with ASTM D6730-01 (2016) and Canadian General Standards Board requirements.
• Assessing column-to-column reproducibility in retention, efficiency, selectivity, peak symmetry, and bleed.
• Demonstrating the effect of hydrogen carrier gas on analysis time and resolution.

Methodology and Instrumentation Used

A high-resolution gas chromatograph with flame ionization detection (GC-FID) was employed. Experimental conditions included:

• Column: Rtx-DHA-100 (100 m × 0.25 mm ID × 0.50 μm) and Rtx-5 DHA tuning column (2–5 m × 0.25 mm ID × 1.00 μm).
• Carrier gas: Hydrogen at constant flow (3.62 mL/min, 55 cm/s linear velocity) or helium for reference.
• Injection: Split 150:1, 0.1 μL, inlet temperature 250 °C, deactivated cup liner.
• Oven program: Initial hold at 5 °C for C5 elution, ramp to 48 °C at 22 °C/min, hold, then gradient to 300 °C.
• Detector: FID at 275 – 300 °C.

Main Results and Discussion

• Inertness and peak shape: Rtx-DHA-100 delivered sharp, symmetric peaks for polar oxygenates (e.g., ethanol, tert-butanol) with predictable retention times, outperforming the competitor column.
• Selectivity: The column achieved baseline separation of critical aromatic pairs (benzene/toluene/p-xylene) and C5–C13 hydrocarbons as required by ASTM D6730-01.
• Reproducibility: Individual testing confirmed consistent retention indices, plate counts exceeding 500 000 for pentane, low tailing factors, and minimal bleed across batches.
• Hydrogen vs. helium: Using hydrogen reduced the total run time from ~146 min to ~71 min (>50% faster) without loss of resolution, effectively doubling sample throughput.

Benefits and Practical Applications

• Enhanced productivity: Laboratories can analyze twice as many samples per day by leveraging hydrogen’s higher allowable linear velocity.
• Cost savings: Hydrogen is less expensive and more accessible than helium, especially when generated on-site.
• Regulatory compliance: Method performance meets or exceeds ASTM and CGSB criteria, ensuring data quality for QA/QC and research.
• Robustness: Columns maintain performance under accelerated temperature programs, making them suitable for high-throughput industrial environments.

Future Trends and Applications

Ongoing developments in stationary phase chemistries and microfluidic GC systems may further reduce analysis times and carrier gas consumption. Integration of high-speed temperature programming and real-time data processing will enhance decision-making in refinery control. Additionally, expanded use of hydrogen generators with embedded safety features can encourage broader adoption of hydrogen-based GC methods in regulated laboratories.

Conclusion

Restek’s Rtx-DHA-100 column demonstrates superior inertness, selectivity, and reproducibility for detailed hydrocarbon analysis of gasoline and oxygenates. The ability to operate with hydrogen carrier gas under accelerated conditions yields over 50% time savings while preserving chromatographic resolution. These advances support faster, cost-effective, and reliable fuel characterization for industrial and research labs.

Reference

1. J.V. Hinshaw, “Frequently asked questions about hydrogen carrier gas,” LC-GC, November 2008.
2. P. Froehlich, “Using hydrogen for gas chromatography,” Lab Manager, vol. 2, 2007, pp. 17.